1. Field of the Invention
This invention relates to a vehicle height control system in which a quantity of air stored in an air chamber associated with an air damper is increased and reduced to adjust the air damper and correspondingly the height of the vehicle.
2. Description of the Related Art
A conventional vehicle height control system is disclosed in the Japanese Patent Laid Open No. 59(1984)-130718. The disclosed vehicle height control system comprises an air damper with an associated expansible air chamber and an air compressor for compressing and pumping the air into the air chamber through a conduit. The vehicle height control system further comprises an air drain valve for discharging to the atmosphere, the air stored in the air chamber, and a cut-off valve for closing the conduit between the air damper and the air compressor.
When operation of the system is initiated to increase the height of the vehicle, the air drain valve is first opened for a predetermined time, during which the compressor remains inoperative and the cut-off valve remains closed, to vent the discharge conduit between the air compressor and the cut-off valve. At the moment operation of the air compressor is started, the air drain valve is closed and the cut-off valve is opened. As a result of reduced air pressure in the discharge conduit, starting operation of the air compressor is facilitated to enable use of a compact electric motor having a small starting torque. Further, when system operation to increase the height of the vehicle is stopped, operation of the air compressor is conventionally stopped at the moment the air drain valve is closed, although this latter operating procedure is not disclosed in the aforementioned Japanese Laid-Open Application.
However, air pressure in the conduit connecting the air damper and the air compressor is suddenly increased when operation of the air compressor is started even though the air pressure generated at that time is extremely low. Therefore, a large amount of vibration is suddenly generated in the vehicle height control system. Further, because the air pressure generated in the conduit connecting the air damper and the air compressor is rather high when operation of the air compressor is stopped, a large amount of vibration is generated at this time of system operation. Therefore, an uncomfortable noise occurs at the vehicle body as a result of the vibrations mentioned being transmitted to the vehicle body.
A rubber antivibration damper disposed between the air compressor and the vehicle body may be set to have a large elastic rate so as to prevent the vibration from being transmitted to the vehicle body. However, a large elastic rate of the rubber antivibration damper causes the vibration generated by the ordinary operation of the air compressor to bring the noise to the vehicle body. When the size of the rubber antivibration damper is increased to prevent the vibration generated when the air compressor is started, stopped and ordinarily operated, from transmission to the vehicle body, the rubber antivibration damper becomes difficult to mount on the vehicle within the small space available.